General routing rules

These rules apply to TCP/IP in general and to TCP/IP on the i5/OS^® operating system.

To manage packets on your system, you should consider these rules as you implement routing functions on your system. These rules can help you determine what is happening to the packets on your system and where they might be going. As with most rules, there are exceptions.

• Your system does not have an IP address; only interfaces have IP addresses.

  Virtual IP (connectionless) addresses are assigned to the system.

• In general, if the destination IP address is defined on your system, your system will process it regardless of what interface a packet comes in on.

  The exception in this case is that if the address is associated with an unnumbered interface, or if IP NAT or filtering is active, the packet might be forwarded or discarded.

• The IP address and mask define the address of the attached network.

• The route out of a system is selected based on the network address attached to an interface. The route selected is based on the following items:

  • Route group search order: direct routes, subnetwork routes, and then default routes.

  • Within a group, the route with the most specific subnet mask is chosen.

  • Equally specific routes are subject to list order or load-balancing techniques.

  • Routes can be added manually or dynamically by the system.

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